Eddy Current Probe (ECP) sensor systems have been used since the 1970's for non-contact displacement measurements, in the monitoring and protection of rotating machines mainly operating with journal (sleeve) bearings. ECP systems are also commonly known as “Proximity Probe Systems”.
Eddy current probes are dependent on a driver comprising an oscillator. The oscillator is used to excite the attached eddy current probe so that it can generate a changing magnetic field. This first magnetic field, when in close range to a steel target material, will induce time changing eddy currents in the surface of the target material. These eddy currents, in turn, will generate a second magnetic field that will oppose the originating first magnetic field and therefore affecting the resulting impedance of the probe tip. The size of the induced eddy currents is dependent on the distance between the probe tip and the steel target material. The probe impedance change is therefore a direct measurement of the distance between the probe tip and the target material. The impedance change as a function of distance is unfortunately not linear. There are many different manners to linearize the impedance change, most of which seem to need manual calibration. There thus seems to be room for improvement.